1. Field of the Invention
The present invention relates to an image processing apparatus and a method of controlling the same.
2. Description of the Related Art
In capturing operation using a capturing apparatus such as a digital still camera or digital video camera, when a scene with large brightness differences is captured, highlight detail loss may occur in a bright portion, and shadow detail loss in a dark portion. As a method of correcting such highlight detail loss and shadow detail loss, there is available a method of generating a high dynamic range image in which bright and dark portions are properly reproduced, by capturing a plurality of images with different exposure amounts, and combining an area without any highlight detail loss with an area without any shadow detail loss in the respective images.
The capturing apparatus disclosed in Japanese Patent Laid-Open No. 2003-046848 can perform capturing while switching between the moving and still image modes. This apparatus generates tone characteristic information by estimating a capturing state from an image having undergone high dynamic range processing, and controls tone characteristics at the time of image reproduction. The capturing apparatus disclosed in Japanese Patent Laid-Open No. 2003-046857 alternately performs long-time capturing and short-time capturing and switches to high dynamic range processing corresponding to the current exposure time. This capturing apparatus also switches combining two images and combining three images in accordance with the degree of similarity to the current frame.
In general, the larger the number of images to be combined with different exposure amounts, the higher the effect of high dynamic range processing. However, the processing requires a long time. Therefore, applying a high dynamic range processing to a moving image or live view image will lead to a decrease in frame rate as the number of images to be combined increases. However, decreasing the number of images to be combined to suppress a decrease in frame rate will lead to large differences in the effect of high dynamic range processing between a preview image and a still image to be recorded which is generated from many images to be combined. It is therefore difficult for the user to check, through a moving image or preview image, the effect of high dynamic range processing in advance for a still image to be recorded.
As described above, various kinds of high dynamic range processing techniques have been proposed. However, neither of the techniques disclosed in Japanese Patent Laid-Open Nos. 2003-046848 and 2003-046857 has proposed any solution for the above problem. In addition, since the capturing apparatus disclosed in Japanese Patent Laid-Open No. 2003-046848 controls tone characteristics at the time of reproduction, a preview image and a reproduced image differ in the effect of high dynamic range processing. Furthermore, the capturing apparatus disclosed in Japanese Patent Laid-Open No. 2003-046857 changes the number of images to be combined and used for high dynamic range processing based on the degree of similarity with respect to motion, and hence it is necessary to prepare resources to always allow processing with the maximum number of images to be combined.